Conventional wisdom dictates that in the 117 motor the guide rails will
break before the chain wears out. I believe the oiling of the chain in
the 117 is superior to that of the 4 and six cylindered cousins. Chain
tensioner should also be checked and replaced.
Another way is to see how far the tensioning device has gone but that is
not a very scientific way of doing it and unless you have a comparative
reference (such as how far the tensioner moved on a new chain) but if
you pull it out and it is just about at the end of it's travel you can
bet your boots that the chain is tired.
Hendrik
Mathieu J. Cama wrote:
[MBZ] 117 timing chain stretch
Tom Savage
Tue, 30 Dec 2008 20:12:28 -0800
Does anyone know how the timing chain stretch is measured on a an M117? This is on a '91 560SEL and I've never been
inside one. Marks on the cam tower like an OM617? I've got to pull the covers as the gaskets are letting oil out all over
the manifold and figure that at 150k miles, I oughta check the (presumed original) chain as well.
Thanks,
Tom
Tom,
Very similar to the om617 in concept and methodology. I like to set the passenger cam to TDC and measure the "stretch"
on the harmonic. If you have no proof the chain has been done, make it simple for yourself: new chain, tensioner, and
all upper guide rails. Cheap insurance in light of an m117 jumping time. It is the guide rails that generally fail. Also,
inspect the sprockets well. These are often worn if the car has seen lackluster maintenance or thin oil. Of course, for a
job like this, genuine MB parts are best. If the upper rails are rather dark, replace the tensioner guide rail as well, but, at
least, ensure you inspect it well. It does like to exhibit grooves into the plastic sheathing and will become brittle, too,
with age. If you are doing all of that, consider a water pump and possibly even a front main seal. Given the age and
mileage, all of these will be due sooner than later. Couple it all together, makes your life simpler in the long run and
makes for less financial expenditure for the customer, too, in the long run. FYI, to time this motor correctly, you really
need to use a dial indicator as indicated in the manuals.
Remember to inspect the passenger cam lobes for wear. Run that motor 2 quarts low on oil and chances are strong that
cam will be damaged. It does not take long to wear a lobe down once the hardening has been compromised.
Lastly, look carefully at the headgaskets at the rear and sides of the motor. These motors are famous for leaking there.
You can attempt to re-torque the heads, but it is not a risk I would recommend taking without a signed waiver.
Have fun, those are great motors and a real joy when correct. The home and Japanese market and ECE variant will knock
your socks off with a true 300hp DIN (117.968, iirc).
Mathieu
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